There was no claim of responsibility, though hardline left-wing activists have attacked the offices before.

The policeman was hit as he sat in a truck outside and taken to hospital, an official from the force said. Three rifle shells were found at the spot.

Small-scale attacks on businesses, police, politicians and embassies are frequent in Greece, which has a long history of political violence and is struggling to emerge from a huge debt crisis which has sent thousands to unemployment and cut incomes.

An organization calling itself the Revolutionary Self-defense Group said it attacked the party's offices in 2014, as part of a move against "the state oligarchy, the dictatorship of the capital and its armed guards".

Democratic Alliance condemned the shooting as a "murderous" attack on democracy.